The Receptor for Advanced Glycated Endproducts (RAGE) is a member of the immunoglobulin superfamily of cell-surface molecules. It was originally identified and characterized as a cellular receptor for glucose (aldose sugar)-modified proteins or Advanced Glycated Endproducts (AGE) (Schmidt et al., J. Biol. Chem. 267: 14987-14997, (1992); Neeper et al., J. Biol. Chem. 267: 14998-15004, (1992)). AGE have been implicated in a variety of disorders associated with diabetes and aging (reviewed in Schmidt et al., Nature Med. 1: 1002-1004, (1995)). Binding of AGE to RAGE induces inflammatory responses in blood vessel walls, which can trigger or aggravate the pathogenesis of macro- or micro-angiopathy.
RAGE has also been reported to interact with other ligands, including amphoterin, a matrix-associated polypeptide that promotes outgrowth of cultured cortical neurons derived from developing brain (Hori et al., J. Biol. Chem. 270: 25752-25761, (1995)). Amphoterin, also known in the literature as high mobility group B1 (HMGB1), has been shown to contribute to a variety of disease states including cancer, inflammatory conditions and sepsis. See Lotze and DeMarco, Curr. Opin. Investig. Drugs 4: 1405-1409 (2003); Scaffidi et al., Nature 418: 191-195 (2002); and Wang et al., Science 285: 248-251 (1999). The expression of RAGE is markedly enhanced and co-localizes with that of amphoterin at the leading edge of advancing neurites, which indicates a potential contribution to cellular migration and in pathologies such as tumor invasion. It has been reported that either anti-RAGE F(ab′)2 or soluble RAGE inhibited neurite outgrowth on amphoterin-coated matrices (Taguchi et al., Nature 405: 354-360, (2000)). Soluble RAGE (sRAGE) is the extracellular domain of the receptor. In addition, blockade of RAGE-amphoterin binding decreased growth and metastases of both implanted tumors and tumors developing spontaneously in susceptible mice, Id.
RAGE has also been identified as a receptor on neurons and microglia for β-amyloid, a polypeptide linked to the pathogenesis of neuronal toxicity and death in Alzheimer's disease (Yan et al., Nature 382: 685-691 (1996)). Expression of RAGE is particularly increased in neurons close to deposits of β-amyloid peptide and to neurofibrillary tangles. In mice, RAGE mediates the transport of human β-amyloid-40 and -42 across the blood-brain barrier (Deane et al., Nature Med. 9: 907-913 (2003)). Inhibition of the RAGE-ligand interaction, either by anti-RAGE IgG or soluble RAGE, neither of which is transported across the blood-brain barrier, suppressed the accumulation of β-amyloid in brain parenchyma in a mouse model of Alzheimer's disease, Id.
RAGE is also a central cell surface receptor for S100A2 and related members of the S100/calgranulins superfamily (Hofmann et al., Cell 97: 889-901 (1999)). Interaction of S100A2 and cellular RAGE on endothelium, mononuclear phagocytes and lymphocytes triggers cellular activation and generation of key proinflammatory mediators. In murine models, blockade of S100A2/RAGE quenched delayed-type hypersensitivity and inflammatory colitis by arresting activation of central signaling pathways and expression of inflammatory gene mediators, Id.
Studies have also shown that binding of RAGE by a ligand triggers activation of key cell signaling pathways, such as p21(ras), MAP kinases, NF-κb, and cdc42/rac thereby reprogramming cellular properties. For example, upon ligand binding, RAGE initiates a signaling cascade that results in the translocation of NF-κb to the nucleus and increased expression of adhesion molecules, procoagulant molecules and inflammatory proteins (Kislinger et al., J. Biol. Chem. 274: 31740-31749 (1999)).
Studies have indicated that RAGE interacts with various molecules implicated in homeostasis, development, inflammation, and certain diseases such as Type 2 diabetes and Alzheimer's disease. Accordingly, it would generally be desirable to block or otherwise inhibit these interactions, when associated with a disease state, to treat or prevent the associated pathologies.
sRAGE has been shown to be efficacious in animal disease models for atherosclerosis, tumor growth and metastasis, colitis, delayed-type hypersensitivity, experimental allergic encephalomyelitis, and Alzheimers disease (Park et al., Nature Med. 4: 1025-1031 (1998); Taguchi et al., supra; Hofmann et al., supra; Yan et al., supra) and can be purified or expressed recombinantly. sRAGE lacks the transmembrane and extracellular domains of full-length RAGE and has three immunoglobulin-like regions: an N-terminal region most similar to an immunoglobulin variable domain (V domain) followed by two regions resembling immunoglobulin constant regions (C domains).
SRAGE has been used extensively in vitro and in vivo to study RAGE-ligand interactions. However, the half-life of sRAGE in rats is 24 hours and therefore sRAGE itself is impractical as a therapeutic for disease. Further, an anti-RAGE IgG would have to bind and inhibit large amounts of RAGE normally expressed in tissues such as lung and may induce death of normal cells. Thus, a need exists for a modified sRAGE that will overcome the short half-life while retaining the AGE binding function of RAGE.